One type of sensor device is a gas sensor device based on the field effect transduction principle. The gas sensor device includes a transducer having a source, a drain, and a gate electrode. A detection circuit is electrically connected to at least the source and the drain of the transducer. In response to the gate electrode being exposed to a target gas, the detection circuit detects an electrical change between the source and the drain that is related to the concentration of the target gas in the vicinity of the gate electrode.
Some gas sensor devices include a gate electrode formed from a layer of porous catalytic metal. The porous catalytic metal has more surface area compared to a solid or non-porous metal layer, such that there is a larger exposure area for the target gas to contact the catalytic material of the gate electrode. As a result, a sensor device having a porous gate electrode has an increased sensitivity level compared to a sensor device having a nonporous gate electrode.
The porous catalytic metal is typically applied to the sensor device in the form of a nanoparticle compound paste. Sometimes, the nanoparticle compound paste is difficult to control, resulting in variations in the thickness and the porosity of the catalytic metal layer. Also, the nanoparticle compound paste is typically applied in a layer that is thicker than desirable (i.e. greater than 1 μm). Furthermore, during a drying/sintering process, the nanoparticle compound paste sometimes cracks and becomes discontinuous.
Accordingly, further developments in forming a porous catalytic metal gate electrode for use as a gas-sensitive portion of a sensor device are desirable.